Production of ferrovanadium alloys

ABSTRACT

A method of producing a low-carbon low-oxygen ferrovanadium alloy by carbon reduction in which an agglomerated mixture of comminuted vanadium oxide, preferably a pentoxide, an iron-source material, and a carbon-source material are heated in vacuum to a temperature of 2,400*-2,800* F. The temperature is maintained until evolution of gas substantially ceases and the product fuses. Additional agglomerate can be charged into the vacuum environment without breaking the vacuum, and molten alloy continuously collected to provide a substantially continuous process.

United States Patent Buker 154] PRODUCTION OF FERROVANADIUM ALLOYS [72] Inventor: Donald 0. Buker, New Concord, Ohio [73] Assignee: Foote Mineral Company, Exton, Pa. [22] Filed: June 10, 1968 [21] Appl. No.: 735,590

[52] US. Cl. ..75/40, 75/49, 75/84, 75/133.5, 75/133 [51] Int. Cl. ..C22c l/00, C22b 55/00 [58] Field of Search ..75/40, 84, 133.5, 133, 49 [56] References Cited UNITED STATES PATENTS 858,325 6/1907 Becket ..75/133 X 1,691,274 11/1928 Flodin et al. ..75/133.5 X 1,699,731 l/l929 Andren ..75/133.5 2,071,942 2/1937 Rohn 75/49 X 2,242,759 5/1941 Schlecht ..75/84 2,256,901 9/1941 Horgard 75/133 X 2,381,675 8/1945 Linz ..75/133 X 2,468,654 4/1949 Brundell et al.. ..75/84 X 2,576,763 11/1951 Linz .7S/133.5 X 3,334,992 8/1967 Downing et al.. ....75/l29 X 3,383,196 5/1968 Carpenter ..75/0.5

3/l970 Guttler et al 3,502,461 ..75/40 3,342,553 9/1967 Buker et al. ..23/208 FOREIGN PATENTS OR APPLICATIONS 529,190 8/1956 Canada OTHER PUBLICATIONS Kroll et al. Reactions of Carbon and Metal Oxides in a Vacuum; Trans. ofElectrochemical Society; (93); June, 1948, pages 247 249; 253- 255.

Hansen; Constitution of Binary Alloys; McGraw-Hill 2nd. Ed.; 1958; p. 730.

Primary Examiner-Henry W. Tarring, ll Attorney-Webb, Burden, Robinson & Webb [57] ABSTRACT 5 Claims, No Drawings PRODUCTION OF FERROVANADIUM ALLOYS This invention relates to a novel method for producing vanadium-iron .alloys and, more particularly, to the production of such alloys having very low carbon and oxygen contents by the carbon reduction of a vanadium oxide.

F errovanadium alloys are well known and have been widely used as addition agents for adding vanadium to steel and iron. Such alloys have been made by aluminothermic reduction of vanadium pentoxide in a refractory lined vessel, by elecof vanadium pentoxide in an electric arc furnace, and by silicon reduction of vanadium pentoxide, usually a two-stage process. These processes produce low-carbon grades of ferrovanadium, generally having a carbon content below about 2 percent and containing 50 to 80 percent vanadium, the balance being iron and possibly small amounts of silicon.

Recently, a solid-state carbon reduction process for the production of a vanadium addition agent has been developed. This process produces a sintered metallic briquette having a relatively low density and containing nominally 85 percent vanadium and 12 percent carbon. Solid-state carbon reduction of vanadium oxide has substantial economic advantages over either aluminum or silicon reduction methods since a much lower cost reducer is used and the power requirements are less. However, in order to keep the residual oxygen content of the product low, that is, less than about 2 percent, it has been necessary to have substantial quantities of residual carbon in the product. In general, if the residual carbon content was lowered to 8 percent or below, the residual oxygen content was 2 percent or higher.

Addition agents having high-carbon contents are not desirable, particularly in the production of lower carbon grades of steel, since they decrease the probability of meeting the narrow specifications for low-carbon steel. Also, if the carbon content of the addition agent is high, the carbon content ofthe steel bath, just prior to alloying additions, must be lower, which results in a higher oxygen content, which can hinder the quality of the steel. Moreover, alloying additions are preferably made in the ladle rather than in the furnace since this permits shorter heat times and better alloy recovery in the steel. Ease of solution of an addition agent naturally favors a more uniform dispersion of the addition in the steel ladle. And, a higher iron content in the addition agent also favors a more uniform dispersion of the alloy in the steel bath, particularly when small additions, for example, 0.04 percent are made. These considerations all favor a low-carbon, high-density ferrovanadium addition agent over the high-carbon, highvanadium, low-density addition agent produced by known carbon reduction techniques.

I have invented a novel process which uses economic solidstate carbon reduction and still yields a low-carbon, high-density ferrovanadium. Specifically, the product of my process is a dense, homogeneous, microscopically clean ferrovanadium in which both the residual carbon and residual oxygen content may be kept less than 2 percent.

Briefly stated, my novel process comprises agglomerating a comminuted mixture of a vanadium oxide, an iron-source material, and a carbon-source material, heating the agglomerated mixture in vacuum to a temperature in the range of about 2,400-2,800 F., and maintaining the temperature and the vacuum until gas evolution substantially ceases and the product fuses and coalesces in a molten pool. l have found that the terminal equilibrium in the solid-state carbon reduction process between carbon and oxygen is altered considerably when vanadium oxide, an iron-source material, such as iron oxide, and a carbon-source material, all of proper particle size, are mixed, agglomerated and vacuum treated. The inclusion of a significant amount of iron-source material apparently permits the oxygen and carbon reaction to proceed nearly to completion with the result that residual carbon contents below 1 percent with residual oxygen contents about 1 percent can be achieved in an alloy using my new process.

The vanadium raw material used in my process is preferably fused vanadium pentoxide V of fine particle size. Vanadium tetroxide (V 0 and vanadium trioxide (V 0 are also satisfactory. The quality of the oxide should be high. The alkali metal and alkaline earth compounds, especially sodium, should be as low as possible, and preferably less than 0.10 percent total. The particle size is preferably less than 60 Tyler mesh, prior to mixing with other ingredients.

The iron-source material can be an oxide, such as F6 0,. Fe O FeO, or a mixture of these oxides. Metallic iron, such as sponge iron of fine particle size, may be used as a source of iron. It should be low in impurities, particularly the oxides of silicon, magnesium, calcium and aluminum. The particle size of the iron-source material should be, preferably, less than 60 Tyler mesh.

The carbon-source material for my process may be graphite, petroleum coke, natural gas coke, or any other similar carbonaceous material of good purity, especially with respect to sulfur. The particle size of the carbon-source material should be fine, preferably less than 200 Tyler mesh. However, a loosely bonded agglomerate is acceptable.

The proportions of the vanadium oxide, iron-source material, and carbon-source material are determined in the first instance by the desired vanadium to iron ratio in the final alloy, which is reached by conventional and well-known calculations. The amount of carbon required for reduction of the vanadium oxides and iron-source material can be calculated but before full-scale production it is desirable to make a series of batch mixtures and reduce them in a laboratory facility. That mixture providing the desired balance of residual carbon to oxygen contents, which can be below about 1 percent carbon and 1 percent oxygen, is then scaled up proportionately for production. When using V 0 the mixture generally will comprise 45 to 70 percent vanadium pentoxide, 15 to 35 percent iron oxide and i5 to 25 percent carbon.

The proper proportions of the V 0 or other vanadium oxide used, iron-source material and carbon-source material are mixed and the mixture agglomerated in the presence of a binder to form a porous article, such as a pellet. Although it is possible to comminute the raw materials to the desired particle size after mixing, this is not very satisfactory because the mixture compacts against the walls of equipment such as a ball mill. The agglomerating step can be carried out satisfactorily with a rotating disc or drum pelletizer. A noncontaminating binder should be used, such as Acrysol or molasses, as is well understood in the art.

When vanadium pentoxide is used as the source of vanadium, the agglomerate should be porous to allow gas to escape quickly during the rapid, exothermic reduction of the pentoxide to the tetroxide. Pellets made on a rotating disc are sufficiently porous for vacuum heating whereas low-porosity, highdensity briquettes made of the same mix in a roll press burst with violence when heated through the temperature range of l,OO01,400 F. It is possible to heat dense briquettes of V 0 through this range without bursting if the heating is carried out in an inert atmosphere such as helium and at near-atmospheric pressure, rather than in a vacuum; however, this is not commercially desirable. Although briquettes including V 0, or V 0 as the source of vanadium may be used, it is preferable to use V 0 because of its lower cost. After pelletizing, the pellets are preferably dried to a relatively low moisture content.

The agglomerated mixture, in the form of pellets or briquettes, is then charged into a suitable facility where it is heated in vacuum to a temperature in the range of about 2,400-2,800 F. Under these conditions, the oxides of vanadium and iron are reduced, liberating carbon monoxide, carbon dioxide and smaller quantities of other gases, which are drawn off by a vacuum pump.

The temperature is maintained until the evolution of gas substantially ceases. The combination of the low-carbon and low-oxygen contents and the low pressure result in fusion of the reduced product without any increase in temperature. The maximum pressure during the reaction should be less than 200 mm. of mercury and the terminal pressure less than about 50 microns of mercury.

Additional agglomerate prepared according to my invention can be charged as reduction and fusion of the product occur, until the collecting container is filled with molten metal. The heating power is turned off and the molten metal is permitted to freeze. Preferably, the vacuum line is closed and an inert helium is introduced into the vacuum chamber while the metal is freezing. The temperature should be below 300 F. before the frozen metal is withdrawn from the furnace.

by a fan through the cooling zone as the product freezes.

The product of the process is a low-carbon, dense-vanadium-bearing alloy which is well suited for use as an addition cent. The balance is iron. The density of the product ranges between 6.75 and 7.10 g./cc.

The following examples illustrate the method of my invention.

EXAMPLE 1 Two mixes were made having the following compositions:

Mix A Mix B V,O 48.14 percent 49.05 percent Mill Scale 32.88 percent 32.18 percent Cabot Coke 18.98 percent 18.77 percent Each mix was ball-milled until the mesh size was substantially -325 Tyler sieve size. The two milled mixes were separately briquetted in a laboratory press and each placed in a high-purity alumina crucible. The crucibles were in turn charged into an electric resistance heated vacuum furnace. and then back-filled with helium. The furnace was heated to 1,450 F., held at this temperature for several minutes, and the furnace evacuated. Heating was continued until each crucible reached 2,700 F., this temperature being maintained for 2 hours during which time the pressure dropped to less than 40 microns. Subsequently, the furnace was permitted to cool to about 200 F.; the crucibles were removed and were found to contain solid buttons of clean metal having the following analyses:

Mix 91 V 7: Fe 4 C A 50.96 44.39 1.83 49.94 45.65 0.28

No direct analysis was made for oxygen because of the difficulty of the method. However, the oxygen content can be closely estimated. The normally unanalyzed residual elements other than oxygen constitute 2 to 2% percent of the product. The total oxygen content of the product is the difference between 100 and the sum of the vanadium, iron and carbon, plus 2 to 2% percent for the other residuals. Thus, in the 0.8 percent, /ygen was between 1.6 and 2.1 percent.

EXAMPLE 11 Additional mixes were made having the following compositions:

Mix C Mix D V 0, 64.30 percent 6364 percent Mill Scale 17.20 percent 16.42 percent Cabot Coke 18.50 percent 1994 percent The mix was ball-milled to approximately 325 Tyler mesh and was then pelletized on a rotating disc using Acrysol as the binder. After oven drying, the pellets were placed in an alumina crucible which was charged into the vacuum furnace of example 1. The furnace was evacuated, then heated to about 2,7002,800 F. After approximately 2 hours, the heating was discontinued and the furnace cooled to ambient temperature. The product was found again to form ofclean, solid metal buttons which analyzed:

Mix 9. v ,4. Fe c '1 0 EXAMPLE 111 than that achieved in example ll, with no The button analyzed as follows:

A substantial number of heats have been successfully made using the carbon reduction method of my invention. In table I the reduction temperature, terminal vacuum, and final chemistry are set forth for several heats made from a mix comprising 49 percent V O 32.20 percent Fe O and 18.80 percent carbon:

TABLE 1 Temp. Terminal Vacuum Final Chemistry "F in Microns Analyzed All of the heats of table 1 resulted in a low-carbon, low-oxygen, dense, clean-ferrovanadium addition agent having a vanadium content of about 50-55 percent. In each instance EXAMPLE IV A mix was prepared in the manner taught herein having a composition of 55.8 percent V 0 42.0 percent Fe O and 18.6 percent carbon. it was heated in an electric resistance vacuum furnace in the manner described above. A terminal vacuum of 80 microns of mercury was obtained. After the product was cooled, it analyzed 53.13 percent vanadium,

43.12 percent iron, and 0.16 percent carbon. The residual ox-- ygen content was estimated to be between 0.6 and 1.1 percent.

While I have described certain preferred embodiments of my invention, it may otherwise be embodied with the scope of the appended claims.

1 claim:

1. A method of producing a ferrovanadium alloy having less than about 1 percent carbon and less than about 1 percent oxygen by carbon reduction of a mixture of vanadium oxide, an iron-source material, and a carbon-source material comprising:

A. comminuting sufficient amounts of vanadium oxide, an iron-source material, and a carbon-source material and forming thereof a finely divided mixture comprising 45-70 percent vanadium pentoxide, 15-35 percent iron oxide and 15-25 percent carbon;

B. agglomerating the mixture;

C. heating the agglomerated mixture in a vacuum to a temperature between about 2,400 and 2,800 F D. maintaining said temperature until gas evolution substantially ceases and the resultant metallic product fuses and coalesces into a molten metal pool; and

E. recovering said ferrovanadium alloy from the pool.

2. The method as set forth in claim 1 wherein the agglomerate of step B is sufficiently porous to permit rapid escape of gas during the heating to prevent bursting of the agglomerate.

3. The method as set forth in claim 1 wherein the particle size of each of the comminuted vanadium oxide, iron-source material, and carbon-source material is less than about 60 Tyler mesh.

4. The method as set forth in claim 2 wherein the fused molten product is maintained in an inert atmosphere until it solidifies and cools to a temperature below about 300 F.

5. The method as set forth in claim 1 wherein additional agglomerated mixture is added to the amounts stated in step A as the volume of said amounts decreases.

Patent No. 5,637,570 January 25, 1972 Dated Donald 0. Buker Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patentare hereby corrected as shown below:

Column 6, line 17, "claim 2" should read claim 1 Signed and sealed this 3rd day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-1050(10-697 USCOMM-DC 60375-P69 fi u.s. GOVERNMENT PRINTING OFFICE 1959 0-3654.

Patent No. 3 a 637 370 Bat-ed January 25 1972 Inventor-(s) Donald 0 er It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 17, "claim 2" Should read claim Signed and sealed this 3 rd day of October 1972.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. ROBERT GOT TSCHALK Attesting Officer Commissioner of' Patents I USCOMM-DC 6O$76-P69 U45. GOVERNMENT PRINTING OFFICE: I989 OJ6,6-83l. 

2. The method as set forth in claim 1 wherein the agglomerate of step B is sufficiently porous to permit rapid escape of gas during the heating to prevent bursting of the agglomerate.
 3. The method as set forth in claim 1 wherein the particle size of each of the comminuted vanadium oxide, iron-source material, and carbon-source material is less than about 60 Tyler mesh.
 4. The method as set forth in claim 1 wherein the fused molten product is maintained in an inert atmosphere until it solidifies and cools to a temperature below about 300* F.
 5. The method as set forth in claim 1 wherein additional agglomerated mixture is added to the amounts stated in step A as the volume of said amounts decreases. 